Free online SRT to SUB converter

Some older media players, DVD tools, and subtitle workflows require MicroDVD .sub files instead of the more common .srt. Converting the file changes millisecond timestamps into frame numbers, so the video's exact frame rate is required for accurate synchronization.

What the SRT format is

SRT is a plain-text subtitle format used by media players, video editors, captioning tools, and streaming workflows. Each subtitle block normally contains a sequence number, a start and end time such as 00:01:12,500 --> 00:01:15,000, caption text, and a blank line.

SRT is easy to create and edit with Subtitle Edit, Aegisub, video software, or a text editor. Its timestamps use hours, minutes, seconds, and milliseconds, but the format does not inherently store the video's frame rate. SRT can also contain basic markup or positioning conventions that different players interpret inconsistently.

What the SUB format is

For text subtitle conversion, SUB usually means MicroDVD. MicroDVD is a plain-text, frame-based format with events such as {125}{190}Caption text. The first number identifies the starting video frame and the second identifies the ending frame. Its advantages are compatibility with some older players and authoring tools, direct alignment with a video's frame timeline, and simple text-based editing.

The .sub extension also identifies VobSub, a different format. VobSub stores rendered bitmap subtitles in a binary .sub file and normally requires a matching .idx file. It is used for extracted DVD subtitles and is not an editable text format. An SRT file cannot become VobSub by changing its extension or rewriting its timestamp syntax.

How to convert SRT to SUB

For a conversion without installing software, use the free converter on 101convert.com:

1. Open the SRT-to-SUB converter on 101convert.com.
2. Upload the .srt file.
3. Choose MicroDVD or text-based SUB if the output format is requested.
4. Enter the video's exact frame rate, such as 23.976, 25, or 29.97 frames per second.
5. Start the conversion and download the resulting .sub file.

For local conversion, Subtitle Edit can export an opened SRT file as MicroDVD:

1. Open Subtitle Edit and select File → Open, then choose the SRT file.
2. Set or confirm the source video's frame rate in the subtitle or video settings when the program requests it.
3. Choose File → Save as and select MicroDVD as the format.
4. Save the output with a .sub extension and test it with the target player.

Use the frame rate reported for the actual video, not a nearby nominal value. Media information tools can identify values such as 24000/1001 (commonly displayed as 23.976), 25, or 30000/1001 (commonly displayed as 29.97).

Quality and compatibility limits

MicroDVD converts millisecond timestamps to whole frame numbers. At 25 fps, one frame lasts 40 milliseconds, so individual subtitle boundaries may move slightly during rounding. A wrong frame rate produces incorrect frame numbers and can cause the subtitles to drift progressively out of sync.

Check line breaks, accented characters, italic markup, and positioning after conversion. MicroDVD supports fewer styling and placement conventions than some SRT-producing applications, and the target player may ignore unsupported tags.

Keep the converted file beside the video with matching base names, for example movie.mp4 and movie.sub, if the player loads external subtitles automatically. If the receiving program specifically expects VobSub, create bitmap subtitles with a DVD-authoring or subtitle-rendering tool and supply the required .idx companion file; renaming a MicroDVD file will not create VobSub.